The present invention relates to a Hall effect angular position sensor utilizing DC input power. It is a sensor used to translate a variable angular position of a shaft to a variable DC voltage. The category of DC in./DC out., shaft angular position sensors can be divided into four groups:
1. Potentiometers, where a DC output voltage measured at a moving contact attached to a rotary shaft, will indicate shaft angular position. PA1 2. DC in./DC out. Rotary variable Differential Transformer (RVDT). The RVDT is an AC in./AC out. device, requiring an alternating current input power source, and its output is an AC voltage. Therefore, a DC in./AC out. converter is required for the excitation of the RVDT and an AC in./DC out. converter is required at its output terminals. PA1 3. DC in./DC out. Rotary Variable capacitor. Electronic circuitry similar to those described in item 2 are required. PA1 4. A shaft angular position sensor utilizing a Hall effect device and a shaft mounted permanent magnet. Shaft rotation will cause a change in the magnetic flux flowing through the Hall effect device, causing a DC output, indicative of shaft angular position. PA1 1. A housing, comprised of a ferromagnetic shell and two ferromagnetic washers. PA1 2. A bobbin assembly comprised of: a tube made of non-magnetic material and three coil forms made of non-conductive, non-magnetic material. PA1 3. Two coils connected in series opposition. PA1 4. A Hall effect device.
Groups Characteristics.
Group 1.
Advantages: Simple design, low cost.
Disadvantages: Moving contact causing mechanical friction between contact and electrical resistance element, resulting in limited life of the sensor. Susceptibility to vibration damage.
Limited Resolution.
Group 2.
Advantages: No contact between rotor and stator. Excellent resolution.
Disadvantages: Complex design. Expensive sensor.
Group 3.
Same as group 2.
Group 4.
Advantages: Simple design. High reliability. Low cost.
Disadvantages: Permanent magnet may be demagnetized, affecting performance and accuracy of the sensor. Adjustment of output voltage and its linearity versus displacement is difficult. The present inventive device may belong in group 4.
Prior art includes U.S. Pat. No. 4,437,019 March 1984, Jacob Chass, Linear Differential Transformer with Constant Amplitude and Variable Phase Output. It includes slanted primary coils, however, "each of said primary windings are extending about secondary windings forming an alternating voltage transformer". Prior art also includes U.S. Pat. No. 3,491,321 January 1970, Jacob Chass, Rotary Variable Differential Transformer used as a sine-cosine Generator. It includes slanted coils. However, "it includes, in combination, an electrical coil providing transformer primary winding and two pairs of slanted secondary coils, providing alternating currents outputs".
Prior art also includes U.S. Pat. No. 4,766,764, August 1985 William L. Trevillion. Magnetic Freepoint Sensor Utilizing Spaced Hall effect Devices. It includes "coil means for marking the inside of drill pipe or tubing with magnetic marks by passing a DC current pulse through said coil means" (claim 1). The ferromagnetic core disposed within the electrical coil is stationary, and is not disposed within the electrical coil for the purpose of indicating mechanical axial displacement.
The principal object of this invention is to provide a Hall effect, shaft angular position sensor that will not be susceptible to external demagnetization of its magnetic element, its core made of `soft` ferromagnetic material (not a permanent magnet).
A further object of the invention is to provide a rotary sensor having means for adjusting the magnitude and polarity of its output voltage over its angular displacement range by varying coil excitation current. A still further object of this invention is to provide a Hall effect, shaft angular position sensor which is simple to design, small in size and inexpensive to produce.